Femtosecond Laser-Based High-Bandwidth Temperature and Species Concentration Measurements in Turbulent Reacting Flows

Advanced measurement techniques that exploit lasers and optics have become well-established tools for characterizing combusting flows.  Such noninvasive measurement approaches are often ideally suited for visualizing complex reacting flows and quantifying key chemical-species concentrations, temperature, and fluid-dynamic parameters.  The fundamental information these techniques provide is essential for achieving a detailed understanding of the chemistry and physics of combustion processes.  These measurement approaches enable fundamental understanding of combustion chemistry and unsteady dynamics in a variety of combustion and propulsion systems for model development and validation.  Our research efforts span a range of activities, from theoretical modeling of  new spectroscopic techniques to optical engineering and miniaturization for the transition to flight-line and in-flight testing.  Although traditional combustion diagnostics based on continuous-wave and nanosecond-pulsed lasers continue to dominate fundamental combustion studies and applications in reacting flows, revolutionary advances in the science and engineering of ultrafast (picosecond- and femtosecond-pulsed) lasers are driving the enhancement of existing diagnostic techniques and enabling the development of new measurement approaches.  The ultrashort pulses afforded by these new laser systems provide unprecedented temporal resolution for studies of chemical kinetics and dynamics, freedom from collisional-quenching effects, and tremendous peak powers for broad spectral coverage and nonlinear signal generation.  The high pulse-repetition rates of ultrafast oscillators and amplifiers allow previously unachievable data acquisition bandwidths for the study of turbulence and combustion instabilities.  The applications of ultrafast lasers for optical measurements in combusting flows and sprays, emphasizing recent achievements and future opportunities will be discussed.